Any person with at least one of the following clinical forms:

Influenza-like illness (ILI)

– Sudden onset of symptoms

AND

– At least one of the following four systemic symptoms:

– Fever or feverishness
– Malaise
– Headache
– Myalgia

AND

– At least one of the following three respiratory symptoms:

– Cough
– Sore throat
– Shortness of breath

Acute respiratory infection (ARI)

– Sudden onset of symptoms

AND

– At least one of the following four respiratory symptoms:

– Cough
– Sore throat
– Shortness of breath
– Coryza

AND

– A clinician’s judgement that the illness is due to an infection

Laboratory Criteria

At least one the following four:

– Isolation of influenza virus from a clinical specimen
– Detection of influenza virus nucleic acid in a clinical specimen
– Identification of influenza virus antigen by DFA test in a clinical specimen
– Influenza specific antibody response

Sub typing of the influenza isolate should be performed, if possible.

Epidemiological Criteria

An epidemiological link by human to human transmission

Case Classification

A. Possible case

Any person meeting the clinical criteria (ILI or ARI)

B. Probable case

Any person meeting the clinical criteria (ILI or ARI) and with an epidemiological link

C. Confirmed case

Any person meeting the clinical (ILI or ARI) and the laboratory criteria